1. Field of the Invention
The present invention relates generally to Digital Subscriber Line (DSL) systems and, more specifically to spectral shaping in DSL systems.
2. Background Art
DSL (Digital Subscriber Line) service, such as Very high bit-rate DSL (VDSL) service, can typically be provided for DSL users located in a building via a DSL system deployed from a cabinet located close to the building or via a DSL system deployed from a cabinet located in the building. In a DSL system deployed from a cabinet located close to the building, fiber is generally deployed to cabinet, which is typically referred to as Fiber-To-The-Node (FTTN) deployment. In a DSL system deployed from a cabinet located in the building, fiber is generally deployed to the cabinet in the building, which is typically referred to as Fiber-To-The-Building (FTTB) deployment. However, cables for the DSL system utilizing FTTN deployment (i.e. an FTTN DSL system) and cables for the DSL system utilizing FTTB deployment (i.e. an FTTB DSL system) typically share the same multi-pair cable in the building. As a result, interference, such as FEXT (Far-End Cross-Talk), can occur between downstream signals in the respective FTTN and FTTB DSL systems, which can cause spectral incompatibility problems between the two systems.
A downstream signal in an FTTN DSL system (i.e. an FTTN downstream signal) originates from a DSL modem (e.g. a VDSL modem) located in a cabinet located outside the building, while a downstream signal in an FTTB DSL system (i.e. an FTTB downstream signal) originates from a DSL modem (e.g. a VDSL modem) located in a cabinet inside the building. As a result, the FTTB downstream signal typically injects a higher level of interference into the FTTN downstream signal than the FTTN downstream signal injects into the FTTB downstream signal. To reduce the level of interference injected into the FTTN downstream signal by the FTTB downstream signal to ensure spectral compatibility between the FTTN and FTTB DSL systems, the FTTB DSL system can be required to employ a technique such as downstream power back-off (DPBO) to appropriately shape the spectrum of the FTTB downstream signal. However, in some situations, such as a situation that exists in Japan, the FTTB DSL system in the building may not be required to employ any downstream signal spectral shaping techniques. Accordingly, there is a need in the art for a method to ensure spectral compatibility between FTTN and FTTB DSL systems that serve DSL users in the same building.